ENDOMORPHIN 1 ACTIVATES NOS 2 ACTIVITY AND
DOWNREGULATES NOS 2 mRNA EXPRESSION
A. ŠARIĆ, T. BALOG*, S. SOBOČANEC AND T. MAROTTI
Division of Molecular Medicine, Rudjer Bošković Institute, Bijenička 54, 10000 Zagreb,
Croatia
*Correspondence to: T. Balog, Division of Molecular Medicine, Rudjer Bošković Institute,
Bijenička 54, 10000 Zagreb, Croatia. Tel.: +385-1-4561-172; fax.: +385-1-4561-010.
E-mail address: balog@irb.hr
Section Editor
1
Abbreviations:
1400W, N-(3-[Aminomethyl]benzyl)acetamidine;
EM, endomorphin;
FCS, fetal calf serum;
ICI-174,864, N,N-diallyl-Tyr-Aib-Aib-Phe-Leu;
L-NMMA, NG-Monomethyl-L-arginine acetate salt;
LPS, lipopolysaccharide;
NO, nitric oxide;
NOS, nitric oxide synthase;
RT-PCR, reverse transcription-polymerase chain reaction;
ß-FNA, ß-Funaltrexamine hydrochloride
2
ABSTRACT
Endomorphins 1 and 2 are newly discovered opioid tetrapeptides whose structure is more
resistant to enzymatic degradation than of other opioid peptides. Endomorphins 1 and 2 are
considered as endogenous ligands with a high affinity for µ receptors. A number of studies
have shown that opioid peptides per se can induce release of nitric oxide from rodent and
human immune cells. Endomorphins seemed to be involved in the process of vasodilatation
by stimulating release of nitric oxide. In our study we stimulated in vitro J774 macrophages
with different concentrations of endomorphin 1 or 2 for measuring nitric oxide release and
nitric oxide synthase 2 mRNA expression. Results showed that 48 h incubation did not
enhance nitric oxide release when measured with the Griess method. On the other hand, using
real-time amperometric detection of nitric oxide release shortly after challenge with
endomorphins, we showed that only 10-6 M endomorphin 1 was able to stimulate nitric oxide
release from a J774 macrophage cell line by activation of NOS 2 izoenzyme. The peak release
was 1000-1500 s after stimulation and was in the range of nitric oxide release stimulated with
10 µg/ml lipopolysaccharide. In contrast to this, endomorphin 2 failed to induce nitric oxide
release in all tested concentrations. Using a specific inhibitor of nitric oxide synthase 2
(1400W) we eliminated the stimulatory effect of endomorphin 1 on nitric oxide release. The
expression of mRNA for nitric oxide synthase 2 in J774 macrophages, after 30 min incubation
with either lipopolysaccharide or 10-6 M endomorphin 1 was not upregulated. As expected,
lipopolysaccharide induced de novo nitric oxide synthase 2 transcription within 4 h. At the
same time, in contrast to lipopolysaccharide, mRNA expression of cells treated with
endomorphin 1 was downregulated. Since a µ-opioid receptor specific antagonist ßFunaltrexamine hydrochloride inhibited nitric oxide release from endomorphin 1 treated cells,
the effect seemed to be µ-opioid receptor mediated.
Key words: nitric oxide, µ-opioid receptor, amperometric detection,
3
INTRODUCTION
Endomorphins 1 and 2 are newly discovered opioid tetrapeptides (Zadina et al., 1997) with a
specific structure which is more resistant to enzymatic degradation than other opioid peptides
such as enkephalins, endorphins or dynorphines (Peter et al., 1999). In contrast to enkephalins
and endorphins which posses low affinity and selectivity to µ-opioid receptors, endomorphins
1 and 2 are considered as endogenous ligands with a high affinity for µ receptors (Zadina et
al., 1997). While endomorphin 1 is more distributed throughout the brain, endomorphin 2
prevails in the spinal cord (Martin-Shild et al., 1999). Both tetrapeptides are detected by
radioimmunoassay and high performance liquid chromatography in cells of the immune
system of rats and humans (Jessop et al., 2000). During infection several authors have noticed
an increase of opioids in peripheral blood as well as on the site of an inflammatory reaction
(Kanjhan, 1995; Stein, 1995). That is to say, under inflammatory conditions various types of
immune cells are able to produce opioid peptides in culture (Sharp and Linner, 1993) and in
situ (Stein et al., 1990). Immune cells from peripheral blood, splenic lymphocytes and
macrophages express mRNA for beta-endorphin and other proopiomelanocortin derived
peptides (Peterson et al., 1993a,b; Eisenstein et al., 1996). Endogenous opioids also modulate
the effect of cytokines on CNS (Hori et al., 1991; Xin and Blatteis, 1991), while on the other
hand cytokines may alter the neural effects of opioids (Jeanjean et al., 1995).
A number of studies have shown that opioid peptides, like enkephalins also induce a release
of nitric oxide (NO) from rodent and human immune cells (Marotti et al., 1998; Balog et al.,
2001; Bengoechea-Alonso et al., 2003; Vujić et al., 2004). Champion et al. (1998)
demonstrated that endomorphins cause vasodilatation in rats by stimulating NO release from
the endothelium.
NO is a molecule involved in the immune, cardiovascular and nervous systems (Moncada et
al., 1988; Magazine et al., 1996). NO is produced from aminoacid L-arginine by an enzyme
4
called nitric oxide synthase (NOS). NOS persists in cells in three different forms: the
endothelial (NOS 3), neuronal (NOS 1) and inducible (NOS 2) form. The first two forms are
constitutively expressed in cells and are Ca2+ dependent as well, while NOS 2 is inducible and
Ca2+ independent (Moncada et al., 1991; Moncada and Higgs, 1993). Constitutive forms of
NOS (endothelial and neuronal) release NO in nM concentration, while the inducible form
(NOS 2) releases NO in µM range (Stefano et al., 2000). NO is primarily a vascular, immune
and neural signalling molecule, being highly effective as general antibacterial and antiviral
agents with the ability to downregulate proinflammatory events (Kubes and Granger, 1992;
Niu et al., 1995; Stefano et al., 1998a).
So far, several studies have shown that inducible NOS 2 can be induced with various signal
molecules and proinflammatory cytokines in vivo (Moncada et al., 1991; Stefano et al.,
1998b).
The aim of this paper was to demonstrate the ability of the J774 macrophages cell line to
release NO upon stimulation with endomorphins 1 and 2, using real-time amperometric
detection of NO release in short-term experiments. Using specific inhibitors of various types
of NOS and opioid receptor antagonists, we aimed to identify the type of NOS involved, and
also the opioid receptor through which NO release was mediated.
5
EXPERIMENTAL PROCEDURES
Reagents
Endomorphins 1 and 2, lipopolysaccharide (LPS), RPMI 1640 without phenol red,
sulphanilamide, N-(1-naphtyl)ethylendiamine dihydrochloride were all purchased from
Sigma, St Louis, USA.
Phenol red-free medium was supplemented with antibiotic/antimycotic (Sigma St. Louis
USA) and used only for Griess assay. For all other assays phenol-red RPMI 1640 medium
(Institute of Immunology, Inc., Zagreb, Croatia) was used.
Preparation of cell cultures
A murine macrophage cell line, J774, was obtained from Pliva, Zagreb, Croatia. Cells were
cultured in 75 cm2 plactic flasks in phenol-red RPMI medium with 10% fetal calf serum
(FCS, Invitrogen, Life Technologies, Carlsbad, CA, USA ) and passed three times a week
until they reached confluency. The cells were maintained in a humidified atmosphere of 95%
air 5% CO2 at 37°C.
Treatment conditions
The J774 cell suspension was seeded into either 24-well flat-bottom plates at 1x106
cells/ml/well for both nitrite assay (Griess) and reverse transcription-polymerase chain
reaction (RT-PCR) experiments, or 2x106 cells/2 ml/well for real-time amperometric
measurements. The J774 cultures were challenged with various concentrations of
endomorphin 1, endomorphin 2 (10-6, 10-7, 10-8, 10-9, 10–10 and 10–11M) or LPS (10 µg/ml).
The cells incubated in the culture medium alone were used as a control. In addition, the cells
were pretreated with either the µ-selective antagonist ß-Funaltrexamine hydrochloride (ßFNA, 10-4 M, Tocris Bioscience, USA) (Vega and Soto, 2003), the δ-selective antagonist
6
N,N-diallyl-Tyr-Aib-Aib-Phe-Leu (ICI-174,864, 10-4 M, Research Biochemicals International
USA)
(Zhang
et
al.,
1992)
or
with
the
NOS
2
selective
inhibitor
N-(3-
[Aminomethyl]benzyl)acetamidine (1400W, 10-4 M, Sigma, St. Louis, USA) (Kalinowski et
al., 2002; Korhonen et al., 2002) for 30 min before the addition of LPS or endomorphins.
Assay for nitrite concentration
Following stimulation for 48 h, with endomorphin 1, endomorphin 2 or LPS, the nitrite
concentration was measured as an indicator of NO production, according to the Griess
reaction (Green et al., 1982).
Briefly, 800 µl of cell culture supernatant was incubated with an equal volume of Griess
reagent (sulfanilamide and N-(1-naphtyl)ethylendiamine dihydrochloride dissolved in 2.5%
H3PO4 as 1% and 0.5% solution, respectively, and mixed in the volume ratio 1:1 immediately
before use) for 15 min at room temperature, in the dark. The optical density was measured
spectrophotometrically at 540 nm. Nitrite concentration was determined using sodium nitrite
as standard (10-100 µM).
Real-time detection of NO
A real-time NO release was measured using the NO detection system ISO-NO MK II with 2
mm diameter NO sensor (World Precision Instruments, Inc., Sarasota, USA). NO diffuses
through a gas-permeable hydrophobic membrane covering the sensor and is oxidized at the
working (Pt) electrode, resulting in an electrical current. This redox current is proportional to
the NO concentration in the sample outside the membrane, and is continuously monitored
with DUO 18 data recording system connected to a PC.
Electrode calibration was performed according to the manufacturer’s instructions. Different
volumes of sodium nitrite standard (NaNO2, 100 µM) were used as a generator of NO. A
7
calibration curve was obtained by measurement of the current, generated by the addition of a
known amount of NaNO2 to produce a known amount of NO. The relationship between the
NO concentration and the output current of the electrode was always linear. Due to the high
sensitivity of the method, a noise of maximum 50 pA amplitude was accepted as background.
For experiments, the tip of the probe was inserted vertically into the 24-well containing 2x106
adherent cells per 2 ml RPMI medium with 10% FCS. Before cell culture treatment, the
sensor probe was allowed to stabilize to achieve NO basal level.
Production of NO was assayed immediately after challenging cells with various
concentrations of endomorphin 1, endomorphin 2 (10-6 to 10-11 M) or LPS (10 µg/ml). For
inhibition studies the effects of endomorphins and LPS were evaluated after 30 min preincubation with a µ-selective opioid receptor antagonist ß-FNA (10-4 M) or NOS inhibitors
NG-Monomethyl-L-arginine acetate salt (L-NMMA 10-4 M, Sigma St Louis USA) and 1400W
(10-4 M).
During the experiment, each culture well was kept on a thermostated block at 37°C.
RNA isolation
At the end of stimulation, the cell monolayer was washed twice with 1 ml of ice-cold
phosphate buffered saline to eliminate excess FCS and nonadherent cells. Total RNA was
extracted using TRIzol reagent (Invitrogen, Carlsbad, CA, USA) according to the
manufacturer’s instructions. Briefly, the cells were lysed directly in the plate wells using 0.5
ml TRIzol reagent per well. After chloroform extraction, the total RNA was recovered from
the aqueous phase and precipitated with an equal volume of isopropanol (Kemika, Zagreb,
Croatia). Total RNA pellet was dissolved in 20 µl of diethylpyrocarbonate (DEPC)-treated
water (Sigma, St. Louis, SAD) after a brief wash with 75% ethanol (Kemika, Zagreb,
8
Croatia). The concentration and integrity of RNA was checked by measuring absorbance at
260 nm followed by electrophoresis on 1% agarose gel (Chomczynski and Sacchi, 1987).
RT-PCR
Of the total RNA, 1 µg was used for reverse transcription reaction in a final volume of 20 µl
with SuperScriptTM II RNase H¯ Reverse Transcriptase (Invitrogen, Life Technologies,
Carlsbad, CA, USA). DNase I pretreatment was used to eliminate contaminating DNA
(Invitrogen, Life Technologies, Carlsbad, CA, USA).
To amplify specific gene product the following primer sequences (5`—3`) were used: NOS 2:
5΄ATG CCC GAT GGC ACC ATC AGA 3΄(forward), 5΄ CAC TTC CTC CAG GAT GTT
GTA 3΄(reverse) and ß-actin: 5΄ GTG GGC CGC TCT AGG CAC CAA 3΄(forward), 5΄ CTC
TTT GAT GTC ACG CAC GAT TTC 3΄(reverse).
These primer sets discriminated between cDNA and genomic DNA due to intronic sequences
and yielded PCR products of 372 and 540 bp for NOS-2 and ß-actin, respectively. Template
cDNA (5 µl) was amplified in a final volume of 25 µl reaction mixture containing 0.5 IU
HotMasterTM Taq DNA polymerase (Eppendorf, Hamburg, Germany), 0.25 mM dNTP Mix,
0.2 mM Mg2+ in 10x Hot Master Taq Buffer and 0.25 µM concentration of each primer. After
initial template denaturation at 94°C for 2 min, amplifications were performed in a
Mastercycler® personal 5332 (Eppendorf, Germany), under the following cycle profile: 94°C
for 35 s, 60°C for 2 min and 72°C for 2 min (NOS 2) or 94°C for 20 s, 55°C for 20 s and
70°C for 40 s (ß-actin). A final step of 10 min at 72°C was performed to complete the PCR
reaction.
For each primer pair, control experiments were performed to determine the range of cycles in
which a given amount of cDNA would be amplified in a linear fashion: 29 cycles for NOS 2,
or 33 cycles for ß-actin.
9
PCR products were subjected to electrophoresis on 1.5% agarose gels, stained with ethidium
bromide and imaged on a UV transilluminator (Image Master VDF, Pharmacia Biotech).
Semiquantitative analysis was performed by measuring the relative optical brightness of each
band. The data were normalized to transcript levels for the constitutive expressed ß-actin
gene, employed as an internal control.
Statistical analysis
Data were analyzed using the statistical package Statgraphic plus 4.0 for Windows, and
reported as mean ± SEM. Statistical comparison between groups was performed using
Analysis of Variance (ANOVA). Post-hoc comparisons were performed using LSD test.
P- value less than 0.05 was considered significant.
10
RESULTS
The effect of endomorphins on nitrite production
To investigate the long-term effect of endomorphins on NO production, J774 macrophages
were challenged with endomorphins (10-6 to 10-10 M) or LPS (10 µg/ml) for 48 h. The
accumulated nitrite was measured in the culture media using Griess reagent. Incubation of
cells with either endomorphin 1 (Fig. 1A) or endomorphin 2 (Fig. 1B) alone did not change
NO release. LPS (10 µg/ml) caused a significant increase (p<0.001) in NO production after a
48 h incubation period.
The effect of endomorphins on NO production
To evaluate the effect of endomorphins on NO production we used the direct real time
amperometric detection method. J774 macrophages were exposed to a concentration gradient
of endomorphins (10-11 to 10-6 M) (Fig. 2). Endomorphin 2 had no effect on NO production
while endomorphin 1 significantly increased (p=0.001) NO only at 10-6 M concentration (Fig.
3). The maximum NO release (390±17 nM compared with medium alone 78±46 nM) was
reached within 1400 sec and did not decline to baseline for at least 1 hour. Endomorphin 1
increased NO release was comparable to LPS (10 µg/ml) induced NO release (405±56 nM) at
the same time (1400 s).
The LPS induced NO release was completely eliminated after 30 min preincubation with NOS
inhibitor L-NMMA (10-4 M) (Fig. 3) demonstrating that the source of NO was due to
enzymatic generation by NOS.
In an attempt to identify which type of NOS is responsible for NO production induced by 10-6
M endomorphin 1, we used selective inhibitor for NOS 2 isoform 1400W. As shown in Fig. 4,
1400W caused a complete inhibition of endomorphin 1 induced NO formation, implying that
the release of NO upon endomorphin 1 stimulation was due to NOS 2 activity. NOS 2
11
inhibitor 1400W alone, no effect on NO release from J774 macrophages was noticed (data not
shown).
Since our results showed NO release within 30 min after stimulation, while NOS 2 synthesis
usually occurs 2-4 h after LPS or cytokine treatment, RT-PCR experiments were performed to
examine the effect on the transcription of NOS 2. As expected, LPS did not induce NOS 2
transcription 30 min post-LPS (Fig. 5A), but within a 4 h incubation period NOS 2
transcription was significantly upregulated (p<0.05) (Fig. 5B). Surprisingly, a significant
amount of NOS 2 mRNA was present in naive unstimulated macrophages after 30 min
incubation with medium alone (control). Similarly to LPS, after 30 min incubation of J774
with endomorphin 1 no significant difference in mRNA expression was detected (Fig. 5A). In
contrast to LPS, endomorphin 1 downregulated NOS 2 expression after 4 h (p<0.05) (Fig.
5B).
A possible involvement of the µ-opioid receptor in endomorphin 1 mediated NO-release was
investigated using µ-opioid receptor selective antagonist ß-FNA. NO release from
endomorphin 1 treated J774 macrophages was partially blocked (46%) using ß-FNA (10-4 M)
pretreatment (Fig. 6). ß-FNA (10-4 M) alone had no effect on NO release from J774
macrophages (data not shown).
12
DISCUSSION
It is known that opioid peptides affect reactive oxygen species release in different cell
systems. Marotti et al. (1990) have shown a donor-dependent upregulation of superoxide
anion release from human neutrophils by opioid peptides, while Šverko et al. (2002)
demonstrated met-enkephalin modulated lipid peroxidation in the liver and thymus of mice.
Met-enkephalin also modulates NO release from peritoneal macrophages in vivo and ex vivo
(Balog et al., 2001; Marotti et al., 1998). LPS and interferon-stimulated NO release from J774
macrophage cell line can be decreased by dynorphin in vitro (Gabrilovac et al., 2003), while
Vujić et al. (2004) have demonstrated that met-enkephalin synergizes with LPS for NO
release from rat peritoneal macrophages. Recently, Lin et al. (2003) provided evidence that
endomorphins can protect human mononuclear blood cells from oxidative damage.
In our study, the J774 macrophage cell line stimulated in vitro with different concentrations of
endomorphin 1 or endomorphin 2 during 48 hours did not enhance NO release when
measured with the Griess method. This might be due to much lower sensitivity of the Griess
assay as compared to amperometric measurement of NO (µM versus nM). That is to say,
since the effects of short-term incubation are most probably related to direct μ-opioid receptor
related effects, a long incubation period might be cytokine release related. These effects of
opioid peptides can be observed in the case of in vivo rather than in vitro opioid peptide
treatment, as we demonstrated in our study (Balog et al., 2001).
Results have shown that only 10-6 M endomorphin 1 stimulated NO release from the J774
macrophage cell line. The peak of release was 1000-1500 s after stimulation and was in the
range of NO release stimulated with 10 µg/ml LPS. In contrast to this, endomorphin 2 in all
tested concentrations failed to induce NO release from J774 mouse macrophages. The
difference might be related to the fact that endomorphin 2 inhibits release of TNF alpha from
macrophages, a cytokine strongly directed to NO release (Azuma and Ohura, 2002). Another
13
possible explanation of the difference between the effective endomorphin 1 and the noneffective endomorphin 2 is the fact that endomorphin 2 is more susceptible to enzymatic
degradation by carboxypeptidase Y than endomorphin 1 (Peter et al., 1999). This is, however,
unlikely since according to our results the stimulation of NO release from J774 macrophages
by endomorphin 1 seems to be µ-opioid receptor mediated. Thus, lack of carboxyterminal
aminoacid probably would not affect our findings. In contrast to that, more impact on the
effect of endomorphin 1 or endomorphin 2 in our study could be caused by the combination
of dipeptydil peptidase IV and aminopeptidase N which affects the aminoterminal side of the
molecule and splitting of aminothermus tyrosine inactivates opioid peptides (Roques et al.,
1993).
The specificity of the measured effect of endomorphin 1 on NO release was demonstrated
using L-NMMA which completely inhibited NOS activity. According to most of the data in
the literature, release of NO from J774 macrophage cell line after short-term stimulation
should be attributed to constitutive NOS isoenzyme. However, since we inhibited the
stimulatory effect of endomorphin 1 on NO release by 1400W, a specific NOS 2 inhibitor in
our study NO release was due to activation of NOS 2 izoenzyme. Also, we detected mRNA
for NOS 2 in unstimulated J774 macrophages. Since de novo NOS 2 synthesis usually occurs
2-4 h after LPS or cytokine treatment, RT-PCR experiments were performed in order to
exclude the possibility that observed NO release after endomorphin 1 treatment was due to de
novo induction of NOS 2 mRNA expression. After 30 min incubation of J774 macrophages
with either LPS or 10-6 M endomorphin 1 we did not notice upregulated mRNA expression for
NOS 2. As expected, LPS-induced de novo NOS 2 transcription became evident within 4 h,
but not 30 min post-LPS. Contrary to LPS, mRNA expression of cells treated with
endomorphin 1 for 4 h was downregulated. However, 4 h after stimulation LPS up-regulated
mRNA for NO, which was followed by a second peak (5-6 h after stimulation) in NO release
14
measured by amperometer. No second peak observed with endomorphin 1 paralleled downregulation in mRNA observed after 4 h stimulation with endomorphin 1 (data not shown).
Besides, the discrepancy between LPS and endomorphin 1 effect might be the result of a
different pathway of macrophage stimulation which, in the case of LPS, involves CD14
activation and for endomorphin 1 μ-opioid receptor activation. Although NO synthesis (by
NOS 2) is mainly regulated at the transcriptional level by the induction of mRNA expression
and there ussualy is a strong correlation between mRNA level and enzyme activity (Jacobs
and Ignarro, 2001; Korhonen et al., 2001; Cho et al., 2003), there are numerous data in the
literature which describe that NOS 2 activity does not follow the up-regulation of NOS 2
mRNA expression and vice versa (Bustamante et al. 1996; Lortie et al., 2000; Nakaya et
al. 2005; Sakai et al., 2006). Therefore, changes in activity which do not correspond to
changes in mRNA level could be due to post-translational regulation of NO synthesis such as
protein stability, dimerization, phosphorylation, cofactor binding and availability of O2 and Larginine as substrates (Pan et al., 1996; Salh et al., 1998; Aktan et al., 2004).
A possible involvement of the µ-opioid receptor in endomorphin 1 mediated NO release was
investigated using µ-opioid receptor selective antagonist ß-FNA. The greatest amount of NO
release from endomorphin 1 treated J774 macrophages was partially blocked by 10-4 M ßFNA (46% inhibition). Thus, the effect of endomorphin 1 on NO release was mostly µ-opioid
receptor mediated. Also, using ICI 174,864 a δ-opioid receptor selective antagonist together
with 10-6 M endomorphin 1 did not inhibit NO release, applying predominantly μ-opioid
receptor involvement.
Taken together, these data lead to conclusion that endomorphin 1 but not endomorphin 2
stimulated NO release shortly (30 min) after challenge by activating inducible NOS (NOS 2)
isoenzyme, and this effect was mostly µ-opioid receptor mediated. No effect of endomorphin
1 or endomorphin 2 was observed probably because in the long incubation period (48 h) the
15
effect would be rather cytokine than μ-opioid receptor related. The similar effects of
cytokines on macrophage activity was demonstrated by Azuma and Ohura (2002).
AcknowledgementsWe thank Vesna Matešić for her excellent technical assistance.
16
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24
TABLES AND FIGURES
nitrite / % of control
A
*
500
450
400
350
300
250
200
150
100
50
0
C
C
LPS
LPS
EM1 -6
EM 1 10-6
EM1 -8 -8 EM1 -10 -10
EM 1 10
EM 1 10
B
900
*
nitrite / % of control
800
700
600
500
400
300
200
100
0
C
C
LPS
LPS
EM2 -6
EM 2 10-6
EM2 -8
EM 2 10-8
EM2 -10 -10
EM 2 10
Fig. 1.
25
3400
EM 1
3200
response/pA
3000
10-7
10-8
10-9
2800
2600
2400
10-11
10-10
2200
2000
1800
1600
1400
0
500
1000
1500
2000
2500
3000
tim e/s
3400
EM 2
3200
10-9
10-6
10-10
10-8
10-7
10-11
3000
response/pA
2800
2600
2400
2200
2000
1800
1600
1400
0
500
1000
1500
2000
2500
3000
tim e/s
Fig. 2.
26
3200
600
LPS
response/pA
3000
NO concentration/nM
500
400
2800
EM 1
2600
Medium
EM 2
2400
LPS+L-NMMA
2200
300
*
0
700
tim e/s
LPS
1400
#
EM 1
Medium
EM 2
LPS+L-NMMA
200
100
0
0
200
600
tim e/s
1000
1400
Fig. 3.
27
600
response/pA
2300
NO concentratio/nM
500
400
EM 1
2200
2100
EM 1+1400W
2000
*
1900
1800
0
1000
300
2000
3000
tim e/s
EM 1
Medium
200
EM 1 + 1400W
100
0
0
200
600
tim e/s
1000
1400
Fig. 4.
28
A
B
C 30
LPS 30
C4
EM 1 30
NOS 2
ß-actin
ß-actin
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
NOS 2/ß-actin ratio
NOS 2/ß-actin ratio
NOS 2
C
LPS
EM 1
LPS 4
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
EM1 4
*
#
C
LPS
EM 1
Fig. 5.
29
600
2500
EM 1
EM 1
response/pA
2200
NO concentration/nM
500
400
EM 1 + ß-FNA
1900
Medium
EM 1 + ß-FNA
*
1600
Medium
1300
1000
300
0
1000
2000
3000
tim e/s
200
100
0
0
200
600
tim e/s
1000
1400
Fig. 6.
30
FIGURE LEGENDS
Fig. 1.
Total nitrite concentration in cell culture supernatant accumulated during 48 h incubation of
J774 macrophages with different concentrations of endomorphin 1 (EM 1) (A), endomorphin
2 (EM 2) (B) (10-6, 10-8 or 10-10 M), LPS (10 µg/ml) or medium alone (control). NO
production was measured using Griess reagent. Results are expressed as mean ± SEM of 3
experiments with individual cultures. Control values are 1.96±0.35 µM for EM 1 and
2.63±0.53 µM for EM 2 experiment.
*p=0.0001 as compared with control.
Fig. 2.
Real time analysis of endomorphin 1 (EM 1) or endomorphin 2 (EM 2) (10-11, 10-10, 10-9, 10-8,
10-7 or 10-6 M) induced NO release by J774 (2x10-6cells/2 ml) macrophages. NO release was
evaluated for 1400 s. Data are representative of each independent culture (n=3-4) which was
subjected to all treatments examined.
Fig. 3.
NO release (nM) during J774 macrophage incubation with 10-6 M EM 1 or EM 2. After a
baseline was established (10 min), cells were challenged with different drugs and the chart
recordings were marked as zero. The NO nanomolar concentrations were calculated from
picoamper current readings based on linear regression equation from standard curve using
NaNO2 solution as standard (1.2041 nM/pA represents the sensitivity of nitric oxide meter
sensor).
Data are expressed as mean ± SEM from 3 to 5 experiments with individual cultures.
*p=0.0001 and #p=0.001 as compared with control media treated cells.
31
Inset, original recordings of the time course of NO release from J774 caused by 10-6 M EM 1.
Fig. 4.
Real time analysis of endomorphin 1 (EM 1, 10-6 M) induced NO release from J774
macrophages inhibited by a selective NOS 2 inhibitor 1400W in J774 cells. 1400W (10-4 M)
was administered 30 min before EM 1.
Data are expressed as mean ± SEM from 2 to 3 experiments using individual cultures.
*p=0.001 compared to control media treated cells.
Inset, original recordings of the time course of NO release.
Fig. 5.
Effect of LPS (10 µg/ml) or 10-6 M EM 1 on NOS 2 mRNA expression in J774 macrophages.
Cells were exposed to EM 1 or LPS (positive control) for 30 min (A) or 4 h (B). A basal
condition of media treated cells served as control. Total RNA was extracted for RT-PCR
amplifications of NOS 2 and ß-actin mRNA.
Top; Electrophoresis of the RT-PCR products is shown via an image of the ethidium bromide
stained agarose gel visualized under UV-transilluminator. The top image shows the
representative results using NOS 2 specific primers, and the bottom image shows the results
for ß-actin.
Bottom; The mRNA bands on the gel photograph were quantified by densitometric analysis
and expressed as NOS 2/ß-actin ratio. Results are representatives from 4 independent cultures
for each group.
*p=0.005 and #p=0.034 as compared with control.
32
Fig. 6.
Real time analysis of attenuated endomorphin 1 (EM 1, 10-6 M) induced NO release by a
selective µ-opioid receptor antagonist ß-FNA in J774 macrophages. ß-FNA (10-4 M) was
administered 30 min before EM 1.
Data are expressed as mean ± SEM from 2 to 3 experiments. *p=0.001 compared with control
media treated cells.
Inset, original recordings of the time course of NO release.
33